1. Field of the Invention
The present invention relates to a liquid crystal display comprising a liquid crystal display controller which controls switching of a liquid crystal screen between normally white and normally black.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Conventionally, normally white liquid crystal screens (hereinafter, also referred to as “NW”) have been used for many portable devices such as a laptop type personal computers. The majority of normally white liquid crystals are twist nematic (TN) liquid crystals which have the problem that their angle of visibility is narrow. In the normally white mode, when a linearly polarized light axis of a first polarizing plate and a linearly polarized light axis of a second polarizing plate cross each other at right angles, and wherein light is transmitted into the liquid crystal display cell through the first and second plates, a voltage is applied to the liquid crystal display cell, and the light is blocked.
FIG. 6 is a block diagram showing a liquid crystal display having a normally white liquid crystal panel. In FIG. 6, input data (digital image input signal) is input into a controller for NW 12, voltage luminance (VT) of the input data is controlled by a data processor, and the input data controlled is input into a liquid crystal driver for NW 22. The liquid crystal driver for NW 22 is fed by a gradation power source 32 and displays images on a liquid crystal panel for NW 42 depending on the input data.
On the other hand, a normally black liquid crystal screen (hereinafter, also referred to as “NB”) have been used for monitors. Particularly, when the screen size is 16 inches or more, the dependency of the angle of visibility increases, therefore, a wide angle of visibility is desired. The majority of normally black liquid crystals are transverse electric field liquid crystals. The problems posed by TN liquid crystals such as a narrow angle of visibility, are solved by adopting a transverse electric field driving type of the liquid crystal cell. However, transverse electric field liquid crystals are manufactured by a more complex process than the manufacturing process for TN liquid crystals, so that the manufacturing costs increase. When a wide angle of visibility is not required, therefore, TN liquid crystals have been used. In the normally black mode, when the linearly polarized light axis of the first polarizing plate and the linearly polarized light axis of the second polarizing plate overlap, a voltage is applied to the liquid crystal display cell, and light is transmitted.
FIG. 7 is a block diagram showing a liquid crystal display having a normally black liquid crystal panel. In FIG. 7, an input data is input to a controller for NB 14, the VT of the input data is controlled by the data processor, and the input data is input to a liquid crystal driver for NB 24. The liquid crystal driver for NB 24 is fed by the gradation power source 34 for the transverse electric field liquid crystal and displays images on an NB liquid crystal panel 44 depending on the input data. The digital image signal input to the NW liquid crystal panel 42 is exactly the opposite of the digital image signal input to the NB liquid crystal panel 44 in polarity. When the controller for NW 12 is combined with an inverter, the controller for NW 12 can function as the controller for NB 14. Furthermore, since TN liquid crystals have a narrow angle of visibility and are not suitable for large screens, TN liquid crystals or transverse electric field liquid crystals are chosen according to the size of the screen panel.
Recent TN liquid crystals have relatively wide angles of visibility by using the optical properties of a sheet for adhering the panels to each other. As a result, the TN liquid crystal can be chosen even if the size of the screen panel is about 18 inch and users can choose either normally white or normally black. However, if controllers for both NW and for NB are provided in a liquid crystal display, the problem that mass production is difficult for the manufacturer arises.
If an NB liquid crystal panel is controlled using the NW controller for NW liquid crystal panel, an arithmetic unit such as an inverter needs to be provided in the NW controller as an NB controller (see Japanese Examined Patent Application, Second Publication, No. Hei 7-46267). As a result, two controllers, one for an NW liquid crystal panel and another for an NB liquid crystal panel, are required, therefore, there is the problem that mass production cannot be carried out.